1. Field of the Invention
The present invention generally relates to a backlight apparatus, and more particularly, to a backlight apparatus that uses a point light source to illuminate a liquid crystal display and so forth.
2. Description of the Related Art
Flat panel displays using liquid crystal panels are recently enjoying popularity as display devices for computer systems. Liquid crystal panels are also used for television systems. Television systems, however, require larger and brighter displays. Accordingly, backlight apparatuses for liquid crystal panels are desired to be brighter and of even brightness.
Generally, liquid crystal displays provided in notebook computers and mobile terminals have backlight apparatuses that illuminate liquid crystal panels from the back. FIGS. 1 and 2 are schematic drawings showing a conventional backlight apparatus 1 disclosed in Japanese Patent Laid-open Application No. 10-283817.
This backlight apparatus 1 includes two point light sources 2, a linear light guide 3, and a plane light guide 4. The point light source 2 is a light emitting diode (LED), for example. The point light source 2 is facing to the incident side face 7 of the linear light guide 3.
The linear light guide 3 and the plane light guide 4 are made of acrylic resin. The light emitted by the point light source 2 travels through the incident side face 7 to the linear light guide 3.
The light traveling through the linear light guide 3 is scattered in the linear light guide 3 and goes out to the plane light guide 4 through the outgoing face 8.
The linear light guide 3 is compatible with an electro luminescent lamp conventionally used to illuminate a liquid crystal panel since the entire portion of the outgoing face 8 of the linear light guide 3 illuminates, that is, the linear light guide 3 behaves as a linear light source. The combination of the point light sources 2 and the linear light guide 3 is preferable because it is less expensive and generates less heat than a conventional linear light source.
The plane light guide 4 is disposed on the back of the liquid crystal panel so that its outgoing face 10 faces the liquid crystal panel. This plane light guide 4 scatters the incident light from the linear light guide 3 through the incident side face 9 so that the light goes out evenly through the entire portion of outgoing face 10 and equally illuminates the entire portion of the liquid crystal panel. Accordingly, the liquid crystal panel is illuminated from the back by the backlight apparatus 1.
The backlight apparatus 1 further includes a first reflector 5 and a second reflector 6. The first reflectors reflects the incident light in the plane light guide 4 so that it does not go out through the side faces but only through the outgoing face 10. The second reflector 6 prevents the leakage of the incident light in the linear light guide 3.
In the case wherein two point light sources such as LEDs are used to reduce the cost of the backlight apparatus, a portion of the light emitted by the point light sources does not go into the linear light guide 3 but leaks since the emitted light spreads spoke-wise (the light will be referred to as the xe2x80x9cleaking lightxe2x80x9d hereinafter).
On the other hand, as showed in FIG. 2, the point light sources 2 and the plane light guide 4 are disposed so closely that a portion of the leaking light enters the plane light guide 4 directly . An arrow 13 showed in FIGS. 1 and 2 indicates the leaking light directly traveling from the point light source 2 to the plane light guide 4. This leaking light goes to a region xe2x80x9cAxe2x80x9d and increases the brightness of the region xe2x80x9cAxe2x80x9d. This degrades the uniformity of brightness.
Accordingly , it is a general object of the present invention to provide a novel and useful backlight apparatus by which one or more of the problems described above are eliminated.
Another and more specific object of the present invention is to provide a backlight apparatus that can ensure uniform brightness.
To achieve the above objects, a backlight apparatus according to the present invention is provided with a point light source that emits rays of light, a linear light guide that is provided by said point light source with said rays of light through an incident side face, diffuses said rays of light there in, and radiates said rays of light through an outgoing side face, said rays of light radiating through said outgoing side face being linearized, a plane light guide that is provided by said linear light guide with said rays of light through an incident side face, diffuses said rays of light therein, and radiates said rays of light through an outgoing face facing an illuminated object, and a light shield unit that prevents a leaking fraction of said rays of light from going directly into said plane light guide.
The leaking fraction of the rays of light is shut out by the light shield unit, and therefore cannot go into the plane light guide. Accordingly, the backlight apparatus according to the present invention can irradiate the illuminated object entirely at an equal brightness.